Conventionally, a gas mixture supplying apparatus for mixing and supplying gases, so-called a gas box or the like, is generally employed when a gas mixture including different kinds of gases is supplied as a processing gas into a region where the gas mixture is used such as a processing chamber of a semiconductor manufacturing apparatus, e.g., when an etching gas is supplied into a processing chamber of a plasma etching apparatus.
The gas mixture supplying apparatus is configured to mix and supply plural gases through a plurality of gas supply lines connected to one common pipeline (manifold) and then to supply the mixture of the gases into the region where the gas mixture is used through a gas mixture supply line via a gas outlet of the common pipeline. Further, conventionally, a gas having a highest flow rate or largest molecular weight is supplied from a gas supply line located closest to the gas outlet, whereas a gas having a lowest flow rate or smallest molecular weight is supplied from a gas supply line located farthest from the gas outlet (see, e.g., Japanese Patent Application Publication No. 1997-283504 and its corresponding U.S. Pat. No. 5,950,675).
However, the present inventors have conducted a research and found that when a higher-flow-rate gas and a lower-flow-rate gas were flowed together at the same time, the higher-flow-rate gas was filled up in the pipeline and impeded a flow of the lower-flow-rate gas, thus resulting in a great delay in arrival time of the lower-flow-rate gas at the processing chamber.